Chemically Bonded Phosphate Ceramics (CBPC), also called “Phosphate Ceramics” are any chemically bonded phosphate compound of cementitious or ceramic nature, generally acquiring final strength at room temperature, but may also be further processed at low heating temperatures (40° C. to 600° C.), low firing temperatures (500° C. to 1000° C.) or by high firing temperatures (above 1000° C.), depending upon the final product application desired. Phosphate ceramics may include various inorganic products/bodies, but the common component is a phosphate compound-metal oxide binder.
CBPCs are typically fabricated by acid-base reactions between an inorganic oxide and either a phosphoric acid solution or a phosphate alkaline salt solution. They are formed by an exothermic reaction producing an early set ceramic-like body. A general example of the reaction is:Oxide+phosphate salt+water→CBPC+heat
One example of a specific reaction is:

The body “sets” at room temperature, it is hard without the need to be fired, and it behaves like a ceramic. Accordingly, the products have been informally called “Cerami-crete” products. Such products have been known for many years, but it is within the last few years that they have surfaced as good candidates to produce fast-setting cements when they are mixed with water and any powdery by-product from many industries. The ability to use powdery by-products provides a new way to recycle and help develop a new “Green Clean Economy.” For example, one research project conducted at Argonne National Labs encased radioactive waste within a solid indestructible paste-rock like material that can be entered in the earth (inside metallic drums) and will not leak harmful components over time.
Other examples of cerami-crete products are manufactured and sold by Bindan Corporation (e.g., Mono-patch®, which is sold and used as a road repair cement), Grancrete, Inc. (e.g., Grancrete™, which can be used as a protective coating or a replacement for concrete), and Ceratech Cement AB (RediMax™ and FireRok™). These materials are generally sold as fast-setting cement paste for cold weather applications using fine sand and Fly Ash C or F as fillers. The same phosphate binder added to styrene beads can be molded into ceiling panels. Adding the binder to gypsum and silicates can form bricks, panels, and other structural materials.
Foamed mixtures of phosphate bonded products may also be used to produce floor tiles, and insulation panels or bricks. These formulations do not add foam per se (e.g., prepared foam) to the mixture. Instead, the porous structure is caused by a chemical reaction among the components that release gases that are trapped in the solid. Additionally, the porosity is typically less than 5%, which results in a hard, solid body, generally having a strength higher than 500 psi (pounds per square inch). These formulations also do not render a structure that is so-called “cellular.” It has been suggested to create a foamed fly ash by adding foam to a mix of Fly Ash F with an alkali as a activator, but the resulting structure is not a cerami-crete because it does not use a phosphate compound and a metal oxide (for example, magnesium oxide) as a binder mix.
Others have experimented with attempts to make a lightweight composite material with CBPC, but those experiments have resulted in CBPC composites with a compressive strength that is quite high (all generally above 100 psi at 24 hours post-mix). Those attempts have also used ammonium phosphate, which has been the preferred phosphate for the past many years, but ammonium phosphate has an adverse environmental impact because of the release of ammonium vapor during the chemical process. It is thus preferable to identify another phosphate material that can be used—one that does not release hazardous vapors into the environment.
Another example of a light weight phosphate cement is one that is manufactured for use as a sealant in heavy oil and CBM (coal bed methane) fields. See, e.g., U.S. Pat. No. 7,674,333. That cement is intended to have a very high compressive strength of at least 500 psi at 24 hours post-mix. The manufacturing process also does not use a foam; the disclosure simply refers to a “foaming agent” that can be added to the composition during the mixing process, not an already prepared foam/pre-foamed product.
In addition to being used as sealants, phosphate ceramic materials have also been used to make rigid, water-resistant phosphate ceramic materials for making tiles with acoustic channeling properties. See, e.g., U.S. Pat. No. 4,978,642. The process for preparing these tiles uses different binder materials and different methods to generate a porous structure than those described herein. Specifically, a chemical reaction is used to produce carbon dioxide gas. Most other references that seek to provide a foamed or lightweight product add a foaming agent or generate a chemical reaction during mixing to produce bubbles (e.g., either they foam through a chemical reaction with carbonate, they produce bubbles by a chemical reaction of decomposing hydrogen peroxide and evaporation of a liquid blowing agent such as Freon (which is environmentally hazardous), they use mechanical mixing to create bubbles, they burn organic materials during the firing process, or they otherwise use environmentally unfriendly materials for the mixtures). The resulting materials also have high tensile strengths of around 140 to about 350 psi, and some are upwards of 500 psi.
Most to all of the strength values reported by the prior art are typically measured at 24 hours post-mix because most of the strength is gained by then. However, the present inventors found a significant increase in strength in those formulations, caused either by curing or drying of the parts beyond one day. This does not particularly matter for these applications, because suggested applications for such materials include insulating panels, construction bricks, refractory materials, foundry filters, decorative structural ceramics, structural materials, floor tiles, and so forth—generally materials for which high strength is desired. Such applications are not concerned with an increase in strength multiple days post-mix—in fact, it is welcomed.
By contrast, if the material is intended for use as a safe and effective vehicle arresting barrier, the strength cannot be beyond the modeled value, or it will cause vehicle damage or endanger the vehicle occupants' lives. It is thus desirable to provide cellular phosphate ceramic materials that can be used for other applications, and thus, that have a lower compressive strength than the above-described materials at the fully-cured/dry state. As mentioned, one specific use that requires a material with a specific compressive strength is in the vehicle arresting technology. The compressive strength for such materials should be such that it absorbs the kinetic energy of a moving vehicle, rendering it effective in stopping the vehicle, but preferably crushing and absorbing the energy to prevent serious injury or death to the vehicle occupants. In other words, the material should be strong enough that it absorbs the vehicle's energy and helps stop the vehicle safely by the system's ability to crush or deform upon impact, and not so strong that it causes the vehicle to crumple against the barrier. The system is intended to cause the vehicle to decelerate more slowly and to provide more cushion than a traditional barrier, and thus, may be referred to in some instances as a “non-lethal” vehicle arresting system. This is one reason why the present application refers to the “fully-cured” material rather than the material at one or two days post-mix. A vehicle arresting barrier cannot be provided that becomes stronger with time—it would render the intent of barrier useless.
One example of a non-lethal vehicle arresting system or compressible vehicle arresting system includes material or a barrier that is placed at the end of a runway that will predictably and reliably crush (or otherwise deform) under the pressure of aircraft wheels traveling off the end of the runway. The resistance provided by the low-strength material decelerates the aircraft and brings it to a stop within the confines of the overrun area. An object of the vehicle arresting system is to fail in a predictable, specified manner, thereby providing controlled, predictable resistive force as the vehicle deforms the vehicle arresting system. A desired vehicle arresting system is thus generally compressible, deformable, crushable, or otherwise able to be compressed or deformed or crushed upon appropriate impact. The material strength should remain constant or at least not increase significantly with time. Specific examples of vehicle arresting systems are called Engineered Materials Arresting Systems (EMAS), and are now part of the U.S. airport design standards described in FAA Advisory Circular 150/5220-22A “Engineered Materials Arresting Systems (EMAS) for Aircraft Overruns” dated Sep. 30, 2005. EMAS and Runway Safety Area planning are guided by FAA Orders 5200.8 and 5200.9.
Alternatively, a compressible (or deformable) vehicle arresting system may be placed on or in a roadway or pedestrian walkway (or elsewhere), for example, for purposes of decelerating vehicles or objects other than aircraft. They may be used to safely stop cars, trains, trucks, motorcycles, tractors, mopeds, bicycles, boats, or any other vehicles that may gain speed and careen out of control, and thus need to be safely stopped.
Embodiments described herein thus provide phosphate ceramic materials that are manufactured using novel methods and that result in specific compressive strength ranges. The materials may be used in a number of applications, but they are particularly suited for use as non-lethal vehicle arresting systems or blast attenuation composite materials.